Agriculture Reference
In-Depth Information
PEPPER SPOT
Apply good cultural practices, including adequate
irrigation and pruning out dead branches and twigs
where the fungus sporulates.
■
Cause
The fungus
Colletotrichum gloeosporioides
.
•
Manage Phytophthora root rot to maintain a healthy
canopy and reduce exposure of fruit to sun damage.
•
Symptoms
Symptoms develop on twigs, pedicels and fruit of the
cultivar, Hass. They appear as superficial, pinhead size,
raised shiny black lesions that may cover the entire fruit.
They occur abundantly on the skin of sun-exposed fruit
where they may form a tear-stain pattern.
PHYTOPHTHORA ROOT ROT
■
Cause
The oomycete
Phytophthora cinnamomi
.
Symptoms
Leaves are pale green, wilted and fall readily. Shoots die back
from the tips so that eventually the tree is reduced to a bare
framework of dying branches. Death of the tree may take from
a few months to several years. Declining trees commonly set
large crops of small fruit. Lack of foliage and dieback of small
branches exposes fruit and major limbs to sunburn.
Source of infection and spread
Infection and spread are discussed under the anthracnose
section.
Importance
Pepper spot causes only superficial blemishes, but can
downgrade fruit quality and, if severe enough, render fruit
unmarketable.
Feeder roots are black, decayed and few in number. Under
healthy trees, white feeder roots are plentiful, particularly at
the interface of the mulch and soil surface.
As infected feeder roots lose the ability to exclude salts, leaf
margins in affected trees develop brown, necrotic
symptoms typical of salt burn.
Management
•
Spray with the recommended fungicide from fruit set to
harvest.
Under severe waterlogging, rapid decline of trees may
occur. The leaves wilt and die, leaving a canopy of brown,
dead leaves.
A weeping stem canker may occur on the lower trunk.
Source of infection and spread
Phytophthora cinnamomi
is a soil inhabitant and requires
aerated water for spore production and infection. Disease
is most severe between 15°C and 27°C.
Fig 4.16 Tree affected by Phytophthora root rot. Symptoms include
wilting, leaf yellowing and sparse foliage.
Fig 4.15 Pepper spot on fruit showing pinhead size spots on the fruit
and pedicel.
